<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>阻止</title>
  <style>
    .cube1 {
      float: left;
      width: 100px;
      height: 100px;
      background-color: red;
    }

    .cube2 {
      /* 他被影响，他设置bfc */
      overflow: hidden;
      width: 200px;
      height: 200px;
      background-color: blue;
    }
  </style>
</head>

<body>
  <div class="cube1"></div>
  <div class="cube2"></div>

</body>

</html>